When the general service pump was started, the pressure built up in the discharge pipe to about 7 bar, which the engineer noticed and relayed to the chief officer. When the pump was shut down, the pressure remained in the pipe because the non-return valve prevented the water from draining back through the pump. When the wheelsman disconnected the cap, it was propelled into his head by the pressure in the pipe. Several factors contributed to this occurrence: system design deficiencies, ineffective crew communication, and inadequate crew familiarization with vessel systems.Analysis When the general service pump was started, the pressure built up in the discharge pipe to about 7 bar, which the engineer noticed and relayed to the chief officer. When the pump was shut down, the pressure remained in the pipe because the non-return valve prevented the water from draining back through the pump. When the wheelsman disconnected the cap, it was propelled into his head by the pressure in the pipe. Several factors contributed to this occurrence: system design deficiencies, ineffective crew communication, and inadequate crew familiarization with vessel systems. System Design In this occurrence, the connect/disconnect design of the piping system used to supply water to the Flume tank required more operator-machine interfaces than a permanent piping system, thereby increasing the opportunity for human error. Moreover, notwithstanding the availability of system feedback to the engineer on watch, the system did not provide adequate feedback to all of the involved crew members as to its state. There was no display information available to the wheelsman to alert him that the water pipe was pressurized before he began to remove the cap, nor was there any information available to the second mate to inform him that the Flume tanks were empty when he had the filling lines disconnected. Had the system provided this information, the actions of the wheelsman and the second mate would likely have been different. Communication Several errors related to communication were evident in this occurrence. In the morning, upon arrival at the port, the master instructed the first mate to connect the Flume tank and place it on standby in readiness for filling, if necessary, depending on the weather and sea conditions outside. On most other occasions the ballast had been taken on in port, prior to departure. When the chief officer did not receive an order to take on ballast following loading, or prior to departure as per usual procedure, he did not seek additional information from the master nor did he communicate to those crew members whose duties or actions could have been affected by the significant change that had occurred in ballasting procedures. The decision on the timing of ballasting was the master's to make. However, because it was not further communicated effectively, the second mate, as well as some other members of the crew, were unaware of the actual status of the vessel. Had the second mate known that ballast was not taken on prior to departure he may not have disconnected the ballast lines and capped the pipe. When the second mate returned to the vessel just prior to departure he did not attempt to communicate with the third mate or the chief officer who was officer of the watch at the time. Had he sought information regarding the status of the vessel from either of them he may have learned that ballast had not yet been taken on. Although it was common practice for the second mate to ensure that the Flume tank filling line was disconnected and that the standing pipe was capped as part of his normal duties, he usually did not perform those duties until specifically told to do so by the chief officer. In addition, whether or not he had been specifically tasked, it was his practice to advise the chief officer if and when those tasks had been completed. Had the second mate adhered to the established work practices, he would have either: not disconnected the filling line and capped the line because he had not been asked to do so, or advised the chief officer what actions had been taken and subsequently would have been told to reconnect the filling line. Because the second mate did not communicate with the chief officer, the chief officer was unaware that the state of the Flume tank filling line had changed. Ineffective communication contributed to this accident in yet another instance. When the chief officer told the engineer on watch to restart the pump, no indication was given to the engineer on watch as to what would have caused the high pressure in the filling line, i.e., that the flexible hose was not connected and/or the line was still capped. Had he relayed this information to the engineer, including his plan to send the wheelsman to connect the lines, probably the engineer would have drained the lines, thereby releasing the line pressure. Conversely, had the engineer on watch sought additional information from the chief officer, his actions might have been different. However, during the communication between the first mate and the engineer on watch, a noise, or alarm sounded, indicating a malfunction in the main engine, distracting, and effectively disrupting the flow of information. Crew Familiarization with Vessel Systems An introduction to basic engineering principles is included in the deck officer certification training program, which the chief officer had successfully completed. The chief officer knew how both a centrifugal pump and a screw down, non-return valve worked. However, he was unaware that such a valve was part of the pumping/piping system used in conjunction with the Flume stabilization system on the CICERO. The chief officer believed that once the centrifugal pump had been shut down, the pressure in the filling line would reduce over a short period of time as the water drained back through the pump. As a result, he did not ask the engineer to drain the lines before he sent the wheelsman to remove the cap from the filling line and to connect the hose. Had he been more familiar with the piping/pumping system, it is probable his actions would have been different. The wheelsman of the MV CICERO was struck in the head by the 10cm quick connect cap from the Flume tank filling line when he removed the cap from the pressurized line. There was a lack of communication between the crew regarding the Flume tank. On deck, there was no method of determining if the capped line was pressurized or if the Flume tanks contained water. The chief officer was unaware that there was a screw down, non-return valve in the Flume tank filling line. Therefore, he incorrectly believed that when the general service pump was stopped the pressure on the line would bleed off over a period of several minutes.Findings The wheelsman of the MV CICERO was struck in the head by the 10cm quick connect cap from the Flume tank filling line when he removed the cap from the pressurized line. There was a lack of communication between the crew regarding the Flume tank. On deck, there was no method of determining if the capped line was pressurized or if the Flume tanks contained water. The chief officer was unaware that there was a screw down, non-return valve in the Flume tank filling line. Therefore, he incorrectly believed that when the general service pump was stopped the pressure on the line would bleed off over a period of several minutes. The wheelsman was injured when he removed the cap from the pressurized ballast line. The Board determined that this wheelsman removed the cap as a result of ineffective crew communication and system design deficiencies in, and inadequate crew familiarization with, the vessel's ballasting system.Causes and Contributing Factors The wheelsman was injured when he removed the cap from the pressurized ballast line. The Board determined that this wheelsman removed the cap as a result of ineffective crew communication and system design deficiencies in, and inadequate crew familiarization with, the vessel's ballasting system. The company reviewed the use of the flexible hose in the Flume tank filling system and determined that a rigid piping system was more suitable. Accordingly, the flexible filling hose was removed and a rigid pipe installed.Safety Action The company reviewed the use of the flexible hose in the Flume tank filling system and determined that a rigid piping system was more suitable. Accordingly, the flexible filling hose was removed and a rigid pipe installed.